docs: def pltnrm(v1, v2, v3):
      """
      Compute an outward normal vector of a triangular plate. 
      The vector does not necessarily have unit length. 
      
      https://naif.jpl.nasa.gov/pub/naif/toolkit_docs/C/cspice/pltnrm_c.html
      
      :param v1: Vertices of a plate.
      :type v1: 3-Element Array of floats
      :param v2: Vertices of a plate. 
      :type v2: 3-Element Array of floats
      :param v3: Vertices of a plate. 
      :type v3: 3-Element Array of floats
      :return: Plate's outward normal vector.
      :rtype: 3-Element Array of floats
      """
      v1 = stypes.toDoubleVector(v1)
      v2 = stypes.toDoubleVector(v2)
      v3 = stypes.toDoubleVector(v3)
      normal = stypes.emptyDoubleVector(3)
      libspice.pltnrm_c(v1, v2, v3, normal)
      return stypes.cVectorToPython(normal)